"In the course of a recent review and upgrade of our security infrastructure, we determined that an unauthorised individual accessed a database of ours that contained usernames, email addresses, and cryptographically protected passwords," said comiXology in a statement.

"Payment account information is not stored on our servers.

"Even though we store our passwords in protected form, as a precautionary measure we are requiring all users to change their passwords on the comiXology platform and recommend that you promptly change your password on any other website where you use the same or a similar password. You can reset your comiXology.com password here.

"We have taken additional steps to strengthen our security procedures and systems, and we will continue to implement improvements on an ongoing basis.

"Please note that we will never ask you for personal or account information in an email, so exercise caution if you receive emails that ask for personal information or direct you to a site where you are asked to provide personal information."